The present invention relates to the field of hydraulic circuits within automatic transmission systems and, more particularly, to a replacement torque converter clutch (hereinafter “TCC”) regulator valve that reduces fluid pressure loss to the torque converter apply and release circuits, which actuate the torque converter clutch.
The General Motors 4L60-E (hereinafter “GM”) transmission and other similar GM transmissions are equipped with mechanisms to “lockup” their torque converters to varying degrees under certain operating conditions. The purpose of the lockup converter is to provide for direct drive when the vehicle is cruising at higher speeds. Since there is always some slippage in the fluid coupling of a torque converter, some power is lost and fuel economy suffers. By providing a direct mechanical coupling through the transmission at high engine speeds, the lockup converter improves fuel economy.
This is accomplished by an electronic/hydraulic torque converter clutch system, which utilizes a lockup piston within the torque converter housing. The lockup piston has friction material on its forward surface. When the vehicle is at cruising speed and lockup is desired, an electric solenoid is energized which opens the torque converter clutch (hereinafter “TCC”) regulator valve. This allows fluid pressure to act upon the lockup piston, which is forced against a machined surface on the converter cover. Thus, the lockup piston and the converter cover are locked together and act as a single unit similar to a manual transmission clutch. When lockup is no longer required, a port opens that allows the pressurized fluid to exhaust. The lockup piston then moves away from the torque converter housing re-establishing the fluid coupling.
Early 4L60E transmissions utilized 2nd gear clutch fluid, which was essentially line pressure applied via an orifice, to actuate the TCC regulator valve. In this version of the transmission, the TCC regulator valve and the isolator valve were combined into one valve. In later versions lockup in the electronic torque converter clutch system was controlled by a pulse width modulated torque converter clutch (hereinafter “PWM TCC”) solenoid that provides an output or control pressure in response to the duty cycle imposed on the solenoid coil.
In 1993 General Motors converted to the PWM actuated TCC regulator valve and divided it into two separate valves, namely the regulator apply valve and the isolator valve. Thus, in the PWM versions (1993–1997) of the 4L60E torque converter, there are actually two converter solenoids being employed in the system. The PWM TCC solenoid sends automatic transmission fluid (hereinafter “ATF”) to the isolator valve. Since the PWM TCC solenoid is duty-cycling the isolator valve, it oscillates continuously within the valve body. The regulator apply valve receives line pressure and regulates it to a lesser pressure, which is known as converter apply pressure. Converter apply pressure is not actually sent to the torque converter, but to the TCC apply valve. The TCC apply valve is actuated by the TCC solenoid. This solenoid is simply an On/Off type solenoid and not a PWM type. It is the TCC apply valve that actually directs ATF to the torque converter.
In 1998 General Motors went to the “EC3” style torque converter. This design allows the torque converter to continuously slip from 2nd gear upward without ever locking up completely. This design was intended to improve fuel economy and converter control. The regulator apply and isolator valves were changed only slightly and function exactly the same as the 1993–1997 PWM version.
A disadvantage associated with these systems is the pulsating flow generated by the pulse width modulated TCC isolator valve as it cycles between its open and closed positions. The isolator valve imparts some of this pulsating movement to the regulator apply valve. These pulsations cause wear within the valve body resulting in hydraulic fluid leakage and incorrect pressure responses. As a result vehicles with a 4L60E transmission often have insufficient TCC apply pressure causing uncontrolled clutch slippage, which overheats the converter and generates TCC slip codes requiring service work. These complaints can often be caused by ATF leakage past the TCC regulator valve resulting in reduced converter apply pressure.
There are known prior art patents that are available in the field and their discussion follows. One example is U.S. Pat. No. 4,271,939 to Iwanga et al. (hereinafter “939 patent”), which discloses a hydraulic control system for a torque converter for ensuring release of the lock-up condition of the torque converter. This is accomplished by providing a flow restrictor in the hydraulic working fluid supply passage for the torque converter to make the flow resistance of the passage equal to or larger than the flow resistance of the hydraulic working fluid supply passage for the lock-up control chamber. In this control system a first or feed passageway communicates with a source of pressurized fluid and with a torque converter chamber, a second or discharge passageway communicates with the torque converter chamber and a third passageway communicates with a lock-up control or clutch chamber of the lockup clutch. A lockup control valve communicates with the same source of pressurized fluid and with the third passageway. The first passageway is provided with the flow restrictor. With the provision of the flow restrictor, the disengagement of the lockup clutch will be assured upon pressurization of the third passageway.
Another example is U.S. Pat. No. 4,618,036 to Ideta (hereinafter “036 patent”), which discloses a hydraulic control system for the lockup clutch of a torque converter wherein release of a lockup clutch is ensured even when the discharge flow rate of the pump is low. This control system comprises a pump driven by an engine to discharge fluid, a torque converter having a lockup clutch with a lockup clutch piston movable to a clutch released position when fluid pressure within a lockup release chamber is higher than fluid pressure within a working chamber in the torque converter cavity, a line pressure regulator valve and an orifice, which provides a restricted flow communication between the torque converter and the pump even when line pressure generated by the line pressure regulator valve is lower than a predetermined value. The Ideta ('036) patent utilizes cutouts 20 formed on the land 32d of the first spool 32 (FIG. 1) on the line pressure regulator valve to permit a sufficient flow of hydraulic fluid via oil conduit 62 to torque converter 10 at low speed operation to ensure the release of the lockup clutch.
While these patents relate generally to hydraulic control systems for torque converters, they do not disclose improving hydraulic control over the torque converter clutch apply circuit or a related method for restoring the hydraulic integrity of such circuits by use of a replacement valve mechanism.
Pending U.S. patent application Ser. No. 09/939,372 to Stafford discloses an actuator feed limit valve (hereinafter “AFL”) assembly comprising a replacement hydraulic valve mechanism for installation within the original equipment valve body of an automatic transmission. The AFL valve directs line pressure into the actuator feed limit circuit, which feeds the shift solenoids, pressure control solenoid and other hydraulically actuated components of the transmission. This valve mechanism utilizes a full contact valve sleeve having inlet and exhaust ports disposed about its circumference, which substantially reduces side loading, bore wear, and AFL fluid circuit leakage. However, this patent application does not disclose the structural improvements and technical advantages of the present invention.